1. Field of the Invention
This invention relates to an integrated optical waveguide device in which thermal spectral shifts are inhibited, and particularly to athermalized optical waveguide devices in which the light transmitting properties are insensitive to temperature variations and fluctuations.
2. Technical Background
Integrated optical waveguide devices, such as integrated optical circuits, combine miniaturized waveguides and optical devices into a functional optical system incorporated onto a small planar substrate. Such integrated optical waveguide devices are utilized in optical communications systems, usually by attaching optical waveguide fibers, that transmit light signals, to the integrated optical waveguide device as inputs and outputs. The integrated optical waveguide device performs a function or process on the transmitted light in the optical communications system. Such devices provide good performance at consistent standard room temperatures but exhibit thermal spectral shifts (d.lambda./dT, measured in nm/.degree. C.) and related poor performance when used in environments where they are exposed to thermal variations and fluctuations in temperature. Integrated optical devices which incorporate interferometers, particularly interferometers based on the division of amplitude, such as Mach-Zehnder interferometers which depend on amplitude splitting of a wavefront, can be used as transmitting filters, sensors, and wavelength multiplexing and demultiplexing devices.
Integrated optical devices which incorporate an interferometer are particularly useful as a wavelength division multiplexer/demultiplexer. Such wavelength multiplexer/demultiplexers may incorporate a phased array comprised of a plurality of different waveguide core arms.
It has been found that the use of integrated optical waveguide devices is limited by their temperature dependence. In such integrated devices, thermal spectral shifts of greater than or of the order of about 0.001 to 0.01 nm/.degree. C. at a transmitting wavelength of 1550 nm can limit their usefulness in environments of differing temperature.